In internal combustion engines utilizing solenoid activated fuel injectors for direct injection into combustion chambers, physical characteristics of the injector solenoid coil are often generally compensated by varying the injector current over the duration of a fuel pulse according to a predetermined injector current profile. One such physical characteristic is the inductive nature of the injector solenoid coil; and a typical such profile may provide an initial rise to a peak current level, in order to open the injector valve as rapidly as possible, followed by one or more periods of maintenance current at lower current levels. Some prior art direct fuel injection systems use a customized injector pulse profile for each injector in order to compensate for the injectors' physical variations from each other.
But the use of different injector current profiles can also be used to optimize fuel pulses to produce different combustion characteristics, particularly in the delivery of multiple consecutive fuel pulses per combustion event in gasoline fueled, direct injected engines. In such multi-pulse delivery, variation of the injector current profiles—and thus the fuel pulse profiles—of consecutive fuel pulses in a single combustion chamber can provide a more precise desired control of the overall fuel delivery to meet more stringent emission and fuel economy goals. Such multi-pulse fuel delivery may be used to produce rapid catalyst light-off or to provide a lean homogeneous fuel mixture.
Fuel injector current profile control directly by a microprocessor in a direct injected engine fuel control system is impractical due to the limited number of available microprocessor output pins, microprocessor throughput constraints, and the inherent communication bandwidth limitations of serial bus communications; and this is especially true for modes of operation in which multi-pulse delivery per combustion event is provided. Thus, fuel injection controls for direct injected, internal combustion engines more typically provide a microprocessor that determines the selected injector, pulse timing, and pulse duration of each injected fuel pulse through dedicated output pins while separate injector current control circuits control the current profiles of the fuel pulses according to internally stored injector current profile defining parameters. Sets of these parameters, with each set tailored for one or more specific injectors, may be programmed into the memory of the microprocessor upon injector installation in the engine and loaded into injector-dedicated registers in the injector control circuits upon each initiation of engine operation. Alternatively, they may be installed directly into registers in the injector current control circuits.
These controls operate reliably for operation as they are designed: wherein a single fuel pulse or multiple fuel pulses are delivered in each combustion event, and the injector current profile of each injector, though potentially different from the others, is unchanging during engine operation. But the provision of different injector current profiles in consecutive multiple fuel pulses in each combustion event requires a much higher communication bandwidth between the microprocessor of the engine fuel control and the injector current control circuits than these controls can reliably provide using affordable current technology.